Electromagnetic valve

ABSTRACT

An electromagnetic valve includes a valve seat, a valving element, and a solenoid part. The valve seat has an annular shape and defines a valve hole. The solenoid part includes a coil, a core guide part, a fixed core, and a movable core. The coil becomes an electromagnet upon energization thereof. The core guide part is arranged radially inward of the coil. The movable core is accommodated and reciprocated inside the core guide part in accordance with whether the electromagnet is turned on or off. The valving element moves integrally with the movable core to open or close the valve hole. The core guide part includes a magnetic unbalance part where magnetic force applied between the core guide part and the movable core is different between on one side and the other side of the core guide part in its radial direction.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. application Ser. No. 13/365,506, filed Feb.3, 2012, which claims priority to Japanese Patent Application No.2011-022509, filed on Feb. 4, 2011, the disclosures of both of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic valve whose valvingelement is actuated by utilizing magnetic force of an electromagnet.

2. Description of Related Art

An example of a conventional normally-closed electromagnetic valve willbe described. In the normally-closed electromagnetic valve, anelectromagnet is produced by energization of a coil. A movable core isattracted to and contacts with a fixed core magnetized by theelectromagnet, so that a valving element attached to the movable core isdisengaged from a valve seat to cause the electromagnetic valve to beopen. When the energization of the coil is stopped and magnetic force ofthe electromagnet disappears, the movable core is pushed back in anopposite direction from the fixed core by reactive force of a returnspring, and the valving element is engaged with the valve seat, therebyto close the electromagnetic valve. In the above-describedelectromagnetic valve, for example, an elastic body such as rubber canbe used for the valving element. In this case, by the repeated openingand closing operation of the valving element for a long period, plasticdeformations such as wear and creep are produced in the valving elementand the valve seat, so that the valving element and the valve seat areshaped to conform to each other. Thus, a sealing performance when thevalving element sits on the valve seat is improved as time passes.However, if the movable core, to which the valving element is attached,rotates while the movable core is attracted and moves to the fixed core,the above-described portions of the valving element and the valve seat,which are conformed in form with each other, are relatively shifted fromeach other. Therefore, the sealing performance when the valving elementsits on the valve seat cannot be maintained.

For the measures against this problem, a technology (see,JP2005-214225A, JP2005-98340A) is known. According to this technology,the movable core is attracted on radially one side of a cylindrical coreguide part for guiding the movable core when the movable core isattracted and moves to the fixed core. In JP2005-214225A, the center ofthe return spring which urges the movable core is eccentrically arrangedrelative to the central axis of the movable core, so that the movablecore is pressed against one side of the core guide part and rotation ofthe movable core is limited. In JP2005-98340A, a gap expansion part,which expands a gap between the movable core and the core guide part, isformed on an outer periphery of the movable core, or an attachmentcenter of an impact absorbing means, which is attached to the movablecore, is made eccentric from the center of the movable core. As aresult, the movable core is pushed against one side of the core guidepart, and rotation of the movable core is prevented.

However, in JP2005-214225A, because an action center of urging force ofthe return spring applied to the movable core is shifted from the centerline of the movable core, a sealing load may be one-sided when thevalving element sits on the valve seat, and leakage from theelectromagnetic valve may occur. In JP2005-98340A, a gravity center ofthe movable core is shifted from the center line of the movable core,i.e., the gravity center is not located on the same line as the centerline of the movable core. Therefore, in the electromagnetic valvedisposed in a vehicle, for example, rotation of the movable core may benot limited due to its install direction, an acceleration of thevehicle, a centrifugal force and so on.

SUMMARY OF THE INVENTION

The present invention addresses at least one of the above disadvantages.

According to the present invention, there is provided an electromagneticvalve including a valve seat, a valving element, and a solenoid part.The valve seat has an annular shape and defines a valve hole that opensradially inward of the valve seat. The valving element is provided to bemovable between a valve-closing position where the valving element isengaged with the valve seat to close the valve hole and a valve-openingposition where the valving element is disengaged from the valve seat toopen the valve hole. The solenoid part is configured to drive thevalving element by utilizing magnetic force of an electromagnet. Thesolenoid part includes a coil, a core guide part, a fixed core, and amovable core. The coil becomes the electromagnet upon energizationthereof. The core guide part has a cylindrical shape and is arrangedradially inward of the coil to form a magnetic circuit. The fixed coreis arranged on one end side of the core guide part in an axial directionof the core guide part and is magnetized by the electromagnet. Themovable core is accommodated inside the core guide part to be opposed tothe fixed core in the axial direction and is reciprocated inside thecore guide part in accordance with whether the electromagnet is turnedon or off. The valving element moves integrally with the movable core toopen or close the valve hole. The core guide part includes a magneticunbalance part where the magnetic force applied between the core guidepart and the movable core is different between on one side and the otherside of the core guide part, which are opposed to each other in a radialdirection of the core guide part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

FIG. 1 is a sectional view illustrating a solenoid part according to afirst embodiment of the invention;

FIG. 2 is a sectional view of the solenoid part illustrating unbalancemagnetic force applied between a core guide part and a movable coreaccording to the first embodiment;

FIG. 3A is a sectional view illustrating the solenoid part excluding themovable core according to the first embodiment;

FIG. 3B is a cross-sectional view taken along a line IIIB-IIIB of FIG.3A and illustrating a magnetic saturation part provided in the coreguide part;

FIG. 4 is a schematic diagram illustrating a fuel vapor treatment systemaccording to the first embodiment;

FIG. 5A is a sectional view illustrating a solenoid part excluding amovable core according to a second embodiment of the invention;

FIG. 5B is a cross-sectional view taken along a line VB-VB of FIG. 5Aand illustrating a magnetic saturation part provided in a core guidepart;

FIG. 6A is a sectional view illustrating a solenoid part excluding amovable core according to a third embodiment of the invention;

FIG. 6B is a cross-sectional view taken along a line VIB-VIB of FIG. 6Aand illustrating a magnetic saturation part provided in a core guidepart;

FIG. 7A is a sectional view illustrating a solenoid part excluding amovable core according to a fourth embodiment of the invention;

FIG. 7B is a cross-sectional view taken along a line VIIB-VIIB of FIG.7A and illustrating a magnetic saturation part provided in a core guidepart; and

FIG. 8 is a perspective view illustrating a movable core according to afifth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Modes of the invention will be in detail described based on embodimentsbelow.

(First Embodiment)

In a first embodiment, an electromagnetic valve of the invention isapplied to a fuel vapor treatment system of a vehicle. As shown in FIG.4, the fuel vapor treatment system prevents fuel vapor from emittinginto the atmosphere. Fuel vapor is evaporated inside a fuel tank 1disposed in the vehicle, The fuel vapor treatment system includes acanister 2 which temporarily adsorbs and holds fuel vapor leaked fromthe tank 1. The canister 2 is filled with an adsorption agent such as anactivated carbon, which adsorbs fuel vapor. The canister 2 includes avapor port 2 a, a purge port 2 b, and an air port 2 c. The vapor port 2a is connected to the tank 1 through a vapor passage 3, and the purgeport 2 b is connected to an intake pipe 5 of an internal combustionengine through a purge passage 4. The air port 2 c opens to theatmosphere through an air passage 6.

A purge valve 7 is provided along the purge passage 4. The purge valve 7regulates a flow volume of fuel vapor, which is suctioned into theintake pipe 5 from the canister 2 by intake negative pressure in theinternal combustion engine. The electromagnetic valve of the inventionis applied to the purge valve 7. A throttle valve 8 is provided in theintake pipe 5. The purge passage 4 is connected to the intake pipe 5 ona downstream side (internal combustion engine-side) of the throttlevalve 8 in an intake-air flow direction. In the air passage 6, a filter9 and a normally-open canister control valve 10 are provided. The filter9 filtrates air flowing into the canister 2, and the canister controlvalve 10 causes the air port 2 c of the canister 2 to be closed asnecessary. The filter 9 can be incorporated into the purge valve 7, and,in this case, the filter 9 provided in the air passage 6 may be omitted.

A structure of the purge valve 7 of the invention will be describedreferring to FIG. 1. The purge valve 7 includes a housing (not shown), avalving element 11, and a solenoid part 12. The housing defines aconnection passage communicating with the purge passage 4. The valvingelement 11 is accommodated inside the housing, and the solenoid part 12actuates the valving element 11 by utilizing magnetic force of anelectromagnet. The connection passage of the housing includes an inflowport, an outflow port, and a communication passage. The inflow port isconnected to the purge passage 4 on an upstream side (canister 2-side)of the purge valve 7 in a flow direction of fuel vapor, and the outflowport is connected to the purge passage 4 on a downstream side (intakepipe 5-side) of the purge valve 7 in the flow direction of fuel vapor.The inflow port and the outflow port communicate with each other throughthe communication passage. An annular valve seat 13 is provided in thecommunication passage. The valving element 11 is made of, for example,rubber elastic body (e.g., fluorine-contained rubber, silicon rubber)and can cause a valve hole 14 to be opened and closed. The valve hole 14opens radially inward of the valve seat 13. When the valving element 11is engaged with the valve seat 13 to close the valve hole 14, acommunication between the inflow port and the outflow port is closed.When the valving element 11 is disengaged from the valve seat 13 to openthe valve hole 14, the communication between the inflow port and theoutflow port is made.

The solenoid part 12 includes a coil 15, a magnetic-circuit formingmember, a movable core 16, and a coil spring 17. The coil 15 is woundaround a bobbin (not shown) having an insulation property, and themagnetic-circuit forming member forms a magnetic circuit around the coil15. The movable core 16 moves in an axial direction of the coil 15 (in avertical direction in FIG. 1), and the coil spring 17 urges the movablecore 16 in one direction. The coil 15 is energized and controlled by anengine control unit (ECU) via a drive circuit (not shown) and becomes anelectromagnet as a result of the supply of an excitation current. Themagnetic-circuit forming member includes a yoke 18, a core guide part19, and a fixed core 20. The yoke 18 is a part of the magnetic circuitlocated on an outer periphery of the coil 15. The core guide part 19 isa part of the magnetic circuit located on an inner periphery of the coil15. The fixed core 20 is located on one side of the core guide part 19in the axial direction of the coil 15. The yoke 18 includes anouter-periphery yoke part and a bottom yoke part. The outer-peripheryyoke part covers the outer periphery of the coil 15 along an entirelength of the coil 15 in the axial direction of the coil 15. The bottomyoke part covers an end surface of the coil 15 on the one side of thecoil 15 in the axial direction.

The core guide part 19 has a cylindrical shape coaxially with the coil15 and defines a guide hole 19 a (see FIG. 3A) in which the movable core16 is contained. An inner surface of the guide hole 19 a is acylindrical surface which has a constant inner diameter entirely in itslongitudinal direction. A core plate 19 b is integrally formed with thecore guide part 19 on an opposite side from the fixed core 20 (on theother side of the core guide part 19) in the axial direction. The coreplate 19 b extends radially outward from the core guide part 19 to havea flange-like shape. The core plate 19 b covers an end surface of thecoil 15 on the other side of the coil 15 in the axial direction and is apart of the magnetic circuit which is connected to the yoke 18. In thecore guide part 19, a magnetic saturation part 21 and a magneticunbalance part 24 are provided. The fixed core 20 serves as anattraction part, which attracts the movable core 16 in the axialdirection due to magnetization of the fixed core 20 by energization ofthe coil 15. As shown in FIG. 1, the fixed core 20 is integrallyprovided with the core guide part 19, but these two can be separatelyprovided from each other.

The movable core 16 is contained in the guide hole 19 a defined by thecore guide part 19, and moves in the guide hole 19 a in the axialdirection (vertical direction in FIG. 1) of the core guide part 19,facing to the fixed core 20. The movable core 16 having a cylindricalshape defines a spring chamber 16 a inside an inner periphery of themovable core 16. An opening of the movable core 16 on an opposite sidethereof from the fixed core 20 is closed by an end board 16 b, to whichthe valving element 11 is attached. An outer circumferential surface ofthe movable core 16 is a cylindrical surface which has a constant outerdiameter entirely in its longitudinal direction. The outer diameter isslightly smaller than the inner diameter of the guide hole 19 a, so thatthe movable core 16 can be reciprocated in the axial direction of thecore guide part 19 in the guide hole 19 a. The coil spring 17 isaccommodated in the spring chamber 16 a of the movable core 16 andlocated coaxially with the movable core 16. An end part of the coilspring 17 on its one end side in an axial direction thereof is supportedby an end surface of the fixed core 20, and an end part of the coilspring 17 on its other end side in the axial direction thereof issupported by the end board 16 b of the movable core 16. Thus, the coilspring 17 urges the movable core 16 in an opposite direction from thefixed core 20 (in an upper direction in FIG. 1), i.e., in a closingdirection in which the valving element 11 is engaged with the valve seat13 to close the valve hole 14.

The magnetic saturation part 21 and the magnetic unbalance part 24,which are provided in the core guide part 19, will be describedreferring to FIGS. 3A and 3B. As shown in FIG. 3A, the magneticsaturation part 21 is provided in the core guide part 19 by forming arecessed part on an entire outer circumference of the core guide part 19in vicinity to the fixed core 20 to reduce a thickness of the core guidepart 19. Thus, the magnetic saturation part 21, where magneticresistance is enhanced by the reduction of a cross-sectional area(thickness) of the magnetic circuit (core guide part 19), is provided inan entire circumference of the core guide part 19. By forming themagnetic saturation part 21 in the core guide part 19, a magnetic fluxflowing directly from the core guide part 19 to the fixed core 20decreases. Hence, a magnetic force applied between the core guide part19 and the movable core 16 increases by the decrease of the magneticflux. Therefore, an attraction force acting between the core guide part19 and the movable core 16 increases.

The magnetic unbalance part 24 is provided such that the magneticcircuit area of the magnetic saturation part 21 provided in the coreguide part 19, i.e., the cross-sectional area of the thickness-reducedpart of the core guide part 19 is different between on one side and theother side of the core guide part 19, which are opposed to each other inthe radial direction of the core guide part 19. That is, magneticforces, which act between the core guide part 19 and the movable core16, on the one side and on the other side of the core guide part 19 inthe radial direction are different from each other. Specifically, asshown in FIG. 3B, the unbalance part 24 is provided at a position wherethe outer diameter center Oa of the core guide part 19 (an innerdiameter center of the guide hole 19 a) is eccentrically locatedrelative to an outer diameter center Ob of the magnetic saturation part21. As indicated by an arrow in FIG. 3A, the magnetic saturation part 21is leaned to the other side (right side in FIG. 3A) of the core guidepart 19 as a whole in the radial direction of the core guide part 19.The cross-sectional area of the magnetic saturation part 21 as themagnetic circuit is not constant along the entire circumference of thecore guide part 19, thereby being smaller on a left side than on a rightside of the core guide part 19 in FIG. 3B.

Magnetic forces, which act between the core guide part 19 and themovable core 16, are different between on the one side and the otherside of the core guide part 19, which are opposed to one another in theradial direction. In the present embodiment, the one side of the coreguide part 19 has a smaller magnetic circuit area than the other sidethereof in the radial direction. Hence, the magnetic force on the oneside of the core guide part 19 more strongly acts between the core guidepart 19 and the movable core 16 than on the other side of the core guidepart 19 in the radial direction. Thus, the movable core 16 is attractedto the one side of the core guide part 19 in the guide hole 19 a. Asdescribed above, the magnetic saturation part 21 is leaned entirely tothe other side of the core guide part 19 in the radial direction.Therefore, as shown in FIG. 3B, the cross-sectional area of the magneticsaturation part 21 as the magnetic circuit (the cross-sectional area ofthe thickness-reduced part) gradually change in a circumferentialdirection of the core guide part 19 without drastically changing betweenthe smallest area part and the largest area part of the magneticsaturation part 21.

An operation and effect of the purge valve 7 of the first embodimentwill be described. The magnetic unbalance part 24 is provided in thecore guide part 19, which is provided in the solenoid part 12 of thepurge valve 7 of the present embodiment. More specifically, thecross-sectional magnetic circuit area of the magnetic saturation part 21(the cross-sectional area of the thickness-reduced part) is smaller onthe one side than on the other side of the core guide part 19 which isopposed to the one side in the radial direction. The saturation part 21functions as the magnetic circuit and is provided for the entirecircumference of the core guide part 19. Consequently, magneticresistance in the magnetic saturation part 21 becomes large on the oneside of the core guide part 19, which has a smaller cross-sectional areaof the magnetic circuit than the other side of the core guide part 19.Therefore, as indicated in thickness of arrows in FIG. 2, the magneticforce, which acts between the core guide part 19 and the movable core16, on the one side of the core guide part 19 becomes large relative tothe magnetic force on the other side of the core guide part 19.

When the movable core 16 is attracted to the fixed core 20 magnetized byenergization of the coil 15, i.e., when the movable core 16 moves in theguide hole 19 a in the axial direction of the core guide part 19, themovable core 16 is attracted to and contacts with the one side of thecore guide part 19 in the radial direction, where magnetic force morestrongly acts on the movable core 16. Accordingly, rotation of themovable core 16 is prevented. Because the unbalance part 24 is notprovided in the movable core 16, a gravity center of the movable core 16is not shifted from a radial center thereof. Therefore, because thegravity center of the movable core 16 is located at the radial centerthereof, rotation of the movable core 16 due to, for example, itsinstall direction with respect to the vehicle, an acceleration of thevehicle, or a centrifugal force does not occur.

The valving element 11 attached to the end board 16 b of the movablecore 16 is always engaged with the same position of the valve seat 13 atclosing time when the valve hole 14 is closed. Hence, as a result of therepeated opening and closing operation of the valving element 11, thevalving element 11 and the valve seat 13 are shaped to conform with eachother, and sealing performance at the closing time is improved. Themovable core 16 is attracted to and contacts with the one side of thecore guide part 19 in the radial direction when the movable core 16moves in the guide hole 19 a. Thus, sliding resistance is producedbetween the movable core 16 and the core guide part 19, and travel speedof the movable core 16 thereby becomes slow. As a result, an impactnoise, which is produced when the movable core 16 contacts with thefixed core 20, is reduced.

(Second Embodiment)

As shown in FIGS. 5A and 5B, a second embodiment is an example in whicha magnetic unbalance part 24 is provided by positioning an innerdiameter center Oc of a guide hole 19 a eccentrically relative to anouter diameter center Oa of a core guide part 19. A magnetic saturationpart 21 is provided in the core guide part 19 such that a recessed partis formed on an outer peripheral surface of the core guide part 19, anda depth of the recessed part is constant along the entire circumferenceof the core guide part 19. That is, the outer diameter center Oa of thecore guide part 19 is located at the same position as a position of anouter diameter center Ob of the magnetic saturation part 21. As shown inFIG. 5B, the inner diameter center Oc of the guide hole 19 a defined bythe core guide part 19 is eccentrically positioned on one side (leftside in FIG. 5A) of the core guide part 19 in a radial direction of thecore guide part 19 with respect to the outer diameter center Oa of thecore guide part 19. Therefore, the entire portion of the guide hole 19 ais formed unevenly on the one side of the core guide part 19 in theradial direction.

A magnetic-path cross-sectional area of the magnetic saturation part 21(a cross-sectional area of a thickness-reduced part) is smaller on theone side than on the other side of the core guide part 19, which isopposed to the one side in the radial direction. The magnetic saturationpart 21 functions as a magnetic circuit and is formed along an entirecircumference of the core guide part 19. Consequently, similar to thefirst embodiment, magnetic resistance in the magnetic saturation part 21is large on the one side of the core guide part 19, which has a smallercross-sectional area of the magnetic circuit than the other side of thecore guide part 19. Therefore, a magnetic force, which acts between thecore guide part 19 and the movable core 16, on the one side of the coreguide part 19 is large relative to a magnetic force on the other side ofthe core guide part 19. When the movable core 16 moves in the guide hole19 a in an axial direction of the core guide part 19, the movable core16 is attracted to and contacts with the one side of the core guide part19 in the radial direction, where magnetic force more strongly acts onthe movable core 16. Thus, rotation of the movable core 16 is prevented.Accordingly, similar effects (e.g., improvement of sealing performanceat valve closing time, and noise abatement) to the first embodiment canbe obtained.

(Third Embodiment)

As shown in FIGS. 6A and 6B, a third embodiment is an example in which amagnetic unbalance part 24 is provided by boring a through hole 22 on acircumferential wall of a core guide part 19. If the through hole 22 isbored on the circumferential wall of the core guide part 19 including amagnetic saturation part 21, a cross-sectional area of the magneticsaturation part 21 as a magnetic circuit is further reduced and magneticresistance increases. As shown in FIG. 6B, if several through holes 22are provided only for one side (left side in FIG. 6A) of the core guidepart 19 in a radial direction of the core guide part 19, magneticresistance on the one side of the magnetic saturation part 21 in theradial direction becomes large relative to magnetic resistance on theother side of the magnetic saturation part 21, which is opposed to theone side in the radial direction. Thus, when a movable core 16 moves inthe guide hole 19 a in an axial direction of the core guide part 19, themovable core 16 is attracted to and contacts with the one side of thecore guide part 19 in the radial direction, where magnetic force morestrongly acts on the movable core 16. Accordingly, rotation of themovable core 16 is prevented. The through hole 22 can be formed by laserradiation, cutting, water jet cutting, or press working, for example. InFIGS. 6A and 6B, several through holes 22 are provided only for the oneside of the core guide part 19, which is opposed to the other side inthe radial direction. However, a magnetic unbalance part 24 can beprovided such that through holes 22 are provided also on the other sideof the core guide part 19 in the radial direction and the number of thethrough holes 22 on the other side is less than the number of thethrough holes 22 on the one side.

(Fourth Embodiment)

A fourth embodiment is another case that a magnetic unbalance part 24 isprovided by boring a through hole 22 on a circumferential wall of a coreguide part 19. In the example of the above-described third embodiment,the several through holes 22 are provided only for the one side of thecore guide part 19, which is opposed to the other side in the radialdirection of the core guide part 19.

However, as shown in FIGS. 7A and 7B, in the fourth embodiment, themagnetic unbalance part 24 is provided by providing the same number ofthe through holes 22 both on one side (left side in FIG. 7A) and theother side of a magnetic saturation part 21, which are opposed eachother in a radial direction of the core guide part 19, and by changingdiameters of the through holes 22. In the example as shown in FIGS. 7Aand 7B, the diameters of the through holes 22 are larger on the one sidethan on the other side of the magnetic saturation part 21 in the radialdirection. Accordingly, magnetic resistance is larger on the one sidethan on the other side of the magnetic saturation part 21 in the radialdirection. Therefore, when a movable core 16 moves in the guide hole 19a in an axial direction of the core guide part 19, the movable core 16is attracted to and contacts with the one side of the core guide part 19in the radial direction, where a magnetic force more strongly acts onthe movable core 16, and rotation of the movable core 16 is prevented.

(Fifth Embodiment)

A fifth embodiment is a case that a coating agent 23 is applied to anouter circumferential surface of a movable core 16, which is attractedto and contacts with one side of a core guide part 19 in a radialdirection of a core guide part 19 when the movable core 16 is attractedto a fixed core 20 and moves in a guide hole 19 a in an axial directionof the core guide part 19. In the first to fourth embodiments, becausethe magnetic resistance is larger on the one side than on the other sideof the core guide part 19 in the radial direction, the movable core 16is attracted to and contacts with the one side of the core guide part19. Accordingly, rotation of the movable core 16 is prevented. In thiscase, when the movable core 16 moves in the guide hole 19 a, the outercircumferential surface of the movable core 16 which slides on an innercircumferential surface of the guide hole 19 a, i.e., a sliding surfaceof the movable core 16 is areally almost fixed. In other words, thesliding surface is within an almost fixed range in a circumferentialdirection of the movable core 16. Thus, as shown in FIG. 8, it is enoughto apply the coating agent 23 only for the sliding surface of themovable core 16, which is attracted to and contacts with the core guidepart 19, and the coating agent 23 need not be applied to the entireouter circumferential surface of the movable core 16. Therefore, aconsumption amount of the coating agent 23 can be reduced.

Modifications of the above embodiments will be described. In the firstembodiment, the electromagnetic valve of the invention is applied to thepurge valve 7 utilized in the fuel vapor treatment system of thevehicle. However, the electromagnetic valve can be applied to thecanister control valve 10. The electromagnetic valve of the inventioncan be applied also to, for example, an hydraulic control valve utilizedin a valve timing control device of an internal combustion engine, or anhydraulic solenoid utilized in an automatic gear shifting device of anvehicle.

To sum up, the electromagnetic valve of the above embodiments may bedescribed as follows.

The electromagnetic valve includes the valve seat 13, the valvingelement 11, and the solenoid part 12. The valve seat 13 has the annularshape and defines the valve hole 14 that opens radially inward of thevalve seat 13. The valving element 11 is movable between thevalve-closing position where the valving element 11 is engaged with thevalve seat 13 to close the valve hole 14 and the valve-opening positionwhere the valving element 11 is disengaged from the valve seat 13 toopen the valve hole 14. The solenoid part 12 drives the valving element11 by utilizing magnetic force of the electromagnet. The solenoid part12 includes the coil 15, the core guide part 19, the fixed core 20, andthe movable core 16. The coil 15 becomes the electromagnet uponenergization thereof. The core guide part 19 has the cylindrical shapeand is arranged radially inward of the coil 15 to form the magneticcircuit. The fixed core 20 is arranged on one end side of the core guidepart 19 in the axial direction of the core guide part 19 and ismagnetized by the electromagnet. The movable core 16 is accommodatedinside the core guide part 19 to be opposed to the fixed core 20 in theaxial direction and is reciprocated inside the core guide part 19 inaccordance with whether the electromagnet is turned on or off. Thevalving element 11 moves integrally with the movable core 16 to open orclose the valve hole 14. The core guide part 19 includes the magneticunbalance part 24 where the magnetic force applied between the coreguide part 19 and the movable core 16 is different between on one sideand the other side of the core guide part 19, which are opposed to eachother in the radial direction of the core guide part 19.

In the electromagnetic valve of the invention, the magnetic unbalancepart 24 is provided in the core guide part 19, which has the cylindricalshape and is a part of the magnetic circuit located radially inward ofthe coil 15. More specifically, the magnetic force applied between themovable core 16 and the core guide part 19 is different between on theone side and the other side of the core guide part 19, which are opposedto each other in the radial direction of the core guide part 19. Thus,when the movable core 16 is attracted to the fixed core 20 by the actionof the electromagnet, i.e., when the movable core 16 moves inside theguide hole 19 a in the axial direction of the core guide part 19, themovable core 16 is attracted to and contacts with one side of the coreguide 19 in the radial direction of the core guide part 19 (the one sideor the other side of the core guide part 19 in the radial direction ofthe core guide part 19) where the magnetic force more strongly acts onthe movable core 16. Hence, rotation of the movable core 16 may beprevented, and accordingly, the valving element 11 moving integrallywith the movable core 16 may be always engaged with the same position ofthe valve seat 13 at closing time when the valve hole 14 is closed.Therefore, the valving element 11 and the valve seat 13 may be shaped toconform to each other, and thereby, the sealing performance at theclosing time can be improved. Additionally, the movable core 16 isattracted to and contacts with one side of the core guide part 19 in theradial direction when the movable core 16 moves inside the core guidepart 19. Thus, sliding resistance is produced between the movable core16 and the core guide part 19. As a result, the travel speed of themovable core 16 becomes slow, and therefore, an impact noise, which isproduced when the movable core 16 contacts with the fixed core 20, canbe reduced.

The core guide part 19 may include the magnetic saturation part 21 alongthe entire outer circumference thereof. The magnetic saturation part 21includes the recessed part on the outer peripheral surface thereof, toreduce the thickness of the core guide part 19, thereby decreasing themagnetic-path cross-sectional area of the magnetic saturation part 21.At the magnetic unbalance part 24, the magnetic-path cross-sectionalarea of the magnetic saturation part 21 is different between on the oneside and the other side of the core guide part 19. In theabove-described structure, as the magnetic-path cross-sectional area ofthe magnetic saturation part 21 is smaller, the magnetic resistance ofthe core guide part 19, which is the part of the magnetic circuit, maybecome larger. Thus, the magnetic force applied between the core guidepart 19 and the movable core 16 may increase. If a magnetic-pathcross-sectional area of one side of the core guide part 19, which isopposed to the other side of the core guide part 19, is made smallerthan a magnetic-path cross-sectional area of the other side of the coreguide part 19, the magnetic force applied between the core guide part 19and the movable core 16 may act larger on the one side than on the otherside of the core guide part 19. Therefore, the movable core 16 can beattracted to the one side of the core guide part 19.

The outer diameter center Ob of the magnetic saturation part 21 may bepositioned eccentrically with respect to the diameter center Oa of thecore guide part 19. When the outer diameter center Ob of the magneticsaturation part 21 coincides with the diameter center Oa, amagnetic-path cross-sectional area of the magnetic saturation part 21 isa constant in the circumferential direction of the core guide part 19.However, if the magnetic saturation part 21 is provided such that theouter diameter center Ob of the magnetic saturation part 21 iseccentrically positioned relative to the diameter center Oa of the coreguide part 19, the magnetic unbalance part 24 can be provided, where themagnetic-path cross-sectional area of the magnetic saturation part 21 isdifferent between the one side and the other side of the core guide part19, which are opposed to each other.

The outer diameter center Ob of the magnetic saturation part 21 maycoincide with the outer diameter center Oa of the core guide part 19.Additionally, the diameter center Oc of the inner peripheral surface ofthe core guide part 19, which accommodates the movable core 16, may belocated eccentrically with respect to the outer diameter center Oa ofthe core guide part 19. Specifically, the inner peripheral surface ofthe core guide part 19 may be shifted to either one side in the radialdirection of the core guide part 19 relative to the outer peripheralsurface of the core guide part 19 (on the one side or the other side ofthe core guide part 19). Accordingly, the magnetic unbalance part 24 canbe provided, where the magnetic-path cross-sectional area of themagnetic saturation part 21 is different between the one side and theother side of the core guide part 19, which are opposed to each other.

At the magnetic unbalance part 24, the core guide part 19 may includethe through hole 22, which passes through the circumferential wall ofthe core guide part 19, only on the one side or the other side of thecore guide part 19. In the above-described structure, because magneticresistance increases, the magnetic force between the movable core 16 andthe core guide part 19 may increase. For example, if the through hole 22is provided only on one side of the core guide part 19, magneticresistance of the one side becomes larger than that of the other side ofthe core guide part 19. Accordingly, the movable core 16 can beattracted to the one side of the core guide part 19, in which themagnetic force applied between the movable core 16 and the core guidepart 19 is relatively strong.

At the magnetic unbalance part 24, each of the one side and the otherside of the core guide part 19 may include at least one through hole 22,which passes through the circumferential wall of the core guide part 19.Moreover, the number of the through holes 22 on the one side of the coreguide part 19 may be different from the number of the through holes 22on the other side of the core guide part 19. In this instance, thenumbers of the through holes 22 passing through the circumferential wallof the core guide part 19 on the one side and on the other side of thecore guide part 19 are different from each other. Hence, a magnitude ofthe magnetic resistance is different between the one side and the otherside of the core guide part 19. For example, when the number of thethrough holes 22 on the one side of the core guide part 19 is largerthan the number of the through holes 22 on the other side of the coreguide part 19 (here, all the hole diameters of the through holes 22 areof the same size), the one side is larger than the other side in themagnitude of the magnetic resistance. Therefore, the movable core 16 canbe attracted to the one side of the core guide part 19, where themagnetic force more strongly acts between the movable core 16 and thecore guide part 19.

At the magnetic unbalance part 24, each of the one side and the otherside of the core guide part 19 may include a through hole 22, whichpasses through the circumferential wall of the core guide part 19.Additionally, a diameter of the through hole 22 on the one side of thecore guide part 19 and a diameter of the through hole 22 on the otherside of the core guide part 19 may be different from each other. In thiscase, the diameters of the through holes 22 passing through thecircumferential wall of the core guide part 19 on the one side and theother side of the core guide part 19, which are opposed to each other,are different from each other. Thus, a magnitude of the magneticresistance is different between the one side and the other side of thecore guide part 19. For example, when the diameter of the through holes22 on the one side of the core guide core 19 is larger than the diameterof the through holes 22 on the other side of the core guide core 19, theone side is larger than the other side in the magnitude of the magneticresistance. Therefore, the movable core 16 can be attracted to the oneside of the core guide part 19, where the magnetic force more stronglyacts between the movable core 16 and the core guide part 19.

The core guide part 19 may include the magnetic saturation part 21 alongan entire outer circumference thereof, and the magnetic saturation part21 includes the recessed part on an outer peripheral surface thereof, toreduce the thickness of the core guide part 19, thereby decreasing themagnetic-path cross-sectional area of the magnetic saturation part 21.Furthermore, the through hole 22 on the one side of the core guide part19 and the through hole 22 on the other side of the core guide part 19are provided at the magnetic saturation part 21. By forming the magneticsaturation part 21 in the core guide part 19, a magnetic flux flowingdirectly from the core guide part 19 to the fixed core 20 decreases.Hence, the magnetic force applied between the core guide part 19 and themovable core 16 increases by the decrease of the magnetic flux.Therefore, an magnetic attraction force acting between the core guidepart 19 and the movable core 16 increases. If the magnetic unbalancepart 24 is provided by boring the through holes 22 at the magneticsaturation part 21, the movable core 16 can be attracted to one side(either side of the one side or the other side of the core guide part 19in its radial direction) of the core guide part 19 on which the magneticforce strongly affects to the movable core 16.

Only a part of the outer peripheral surface of the movable core 16,which slides on the inner peripheral surface of the core guide part 19,may be coated with the coating agent 23. In the electromagnetic valve ofthe invention, when the movable core 16 is attracted to the fixed core20 and moves inside the core guide part 19 due to the action of theelectromagnet, the movable core 16 is attracted to and contacts with oneside of the core guide part 19 (either side of one side or the otherside of the core guide part 19 in the radial direction), the movablecore 16 thereby being prevented from rotating. In this case, the outercircumferential surface of the movable core 16 which slides on the innercircumferential surface of the core guide part 19, i.e., the slidingsurface of the movable core 16 is areally almost fixed. In other words,the sliding surface is within an almost fixed range in a circumferentialdirection of the movable core 16. Thus, the coating agent 23 need not beapplied to the entire outer circumferential surface of the movable core16, and it is enough to apply the coating agent 23 only for the slidingsurface of the movable core 16. Therefore, the consumption amount of thecoating agent 23 can be reduced.

Additional advantages and modifications will readily occur to thoseskilled in the art. The invention in its broader terms is therefore notlimited to the specific details, representative apparatus, andillustrative examples shown and described.

What is claimed is:
 1. An electromagnetic valve comprising: a valve seathaving an annular shape and defining a valve hole that opens radiallyinward of the valve seat; a valving element provided to be movablebetween a valve-closing position where the valving element is engagedwith the valve seat to close the valve hole and a valve-opening positionwhere the valving element is disengaged from the valve seat to open thevalve hole; and a solenoid part configured to drive the valving elementby utilizing magnetic force of an electromagnet, wherein: the solenoidpart includes: a coil which becomes the electromagnet upon energizationthereof; a core guide part which has a cylindrical shape and is arrangedradially inward of the coil to form a magnetic circuit; a fixed corewhich is arranged on one end side of the core guide part in an axialdirection of the core guide part and is magnetized by the electromagnet;and a movable core which is accommodated inside the core guide part tobe opposed to the fixed core in the axial direction and which isreciprocated inside the core guide part in accordance with whether theelectromagnet is turned on or off; the valving element moves integrallywith the movable core to open or close the valve hole; the core guidepart includes a magnetic unbalance part where the magnetic force appliedbetween the core guide part and the movable core is different between onone side and the other side of the core guide part, which are opposed toeach other in a radial direction of the core guide part; and at themagnetic unbalance part, the core guide part includes a through hole,which passes through a circumferential wall of the core guide part, onlyon the one side or the other side of the core guide part.
 2. Theelectromagnetic valve according to claim 1, wherein: the core guide partincludes a magnetic saturation part along an entire outer circumferencethereof; the magnetic saturation part includes a recessed part on anouter peripheral surface thereof, to reduce a thickness of the coreguide part, thereby decreasing a magnetic-path cross-sectional area ofthe magnetic saturation part; and the through hole is provided at themagnetic saturation part.
 3. An electromagnetic valve comprising: avalve seat having an annular shape and defining a valve hole that opensradially inward of the valve seat; a valving element provided to bemovable between a valve-closing position where the valving element isengaged with the valve seat to close the valve hole and a valve-openingposition where the valving element is disengaged from the valve seat toopen the valve hole; and a solenoid part configured to drive the valvingelement by utilizing magnetic force of an electromagnet, wherein: thesolenoid part includes: a coil which becomes the electromagnet uponenergization thereof; a core guide part which has a cylindrical shapeand is arranged radially inward of the coil to form a magnetic circuit;a fixed core which is arranged on one end side of the core guide part inan axial direction of the core guide part and is magnetized by theelectromagnet; and a movable core which is accommodated inside the coreguide part to be opposed to the fixed core in the axial direction andwhich is reciprocated inside the core guide part in accordance withwhether the electromagnet is turned on or off; the valving element movesintegrally with the movable core to open or close the valve hole; thecore guide part includes a magnetic unbalance part where the magneticforce applied between the core guide part and the movable core isdifferent between on one side and the other side of the core guide part,which are opposed to each other in a radial direction of the core guidepart; at the magnetic unbalance part, each of the one side and the otherside of the core guide part includes at least one through hole, whichpasses through a circumferential wall of the core guide part; and anumber of the at least one through hole on the one side of the coreguide part is different from a number of the at least one through holeon the other side of the core guide part.
 4. The electromagnetic valveaccording to claim 3, wherein: the core guide part includes a magneticsaturation part along an entire outer circumference thereof; themagnetic saturation part includes a recessed part on an outer peripheralsurface thereof, to reduce a thickness of the core guide part, therebydecreasing a magnetic-path cross-sectional area of the magneticsaturation part; and the at least one through hole on the one side ofthe core guide part and the at least one through hole on the other sideof the core guide part are provided at the magnetic saturation part. 5.An electromagnetic valve comprising: a valve seat having an annularshape and defining a valve hole that opens radially inward of the valveseat; a valving element provided to be movable between a valve-closingposition where the valving element is engaged with the valve seat toclose the valve hole and a valve-opening position where the valvingelement is disengaged from the valve seat to open the valve hole; and asolenoid part configured to drive the valving element by utilizingmagnetic force of an electromagnet, wherein: the solenoid part includes:a coil which becomes the electromagnet upon energization thereof; a coreguide part which has a cylindrical shape and is arranged radially inwardof the coil to form a magnetic circuit; a fixed core which is arrangedon one end side of the core guide part in an axial direction of the coreguide part and is magnetized by the electromagnet; and a movable corewhich is accommodated inside the core guide part to be opposed to thefixed core in the axial direction and which is reciprocated inside thecore guide part in accordance with whether the electromagnet is turnedon or off; the valving element moves integrally with the movable core toopen or close the valve hole; the core guide part includes a magneticunbalance part where the magnetic force applied between the core guidepart and the movable core is different between on one side and the otherside of the core guide part, which are opposed to each other in a radialdirection of the core guide part; at the magnetic unbalance part, eachof the one side and the other side of the core guide part includes athrough hole, which passes through a circumferential wall of the coreguide part; and a diameter of the through hole on the one side of thecore guide part and a diameter of the through hole on the other side ofthe core guide part are different from each other.
 6. Theelectromagnetic valve according to claim 5, wherein: the core guide partincludes a magnetic saturation part along an entire outer circumferencethereof; the magnetic saturation part includes a recessed part on anouter peripheral surface thereof, to reduce a thickness of the coreguide part, thereby decreasing a magnetic-path cross-sectional area ofthe magnetic saturation part; and the through hole on the one side ofthe core guide part and the through hole on the other side of the coreguide part are provided at the magnetic saturation part.
 7. Theelectromagnetic valve according to claim 1, wherein the core guide partincludes multiple through holes, which each pass through acircumferential wall of the core guide part in a same circumference ofthe core guide part in an axial direction.
 8. The electromagnetic valveaccording to claim 3, wherein the core guide part includes multiplethrough holes, which each pass through a circumferential wall of thecore guide part in a same circumference of the core guide part in anaxial direction.
 9. The electromagnetic valve according to claim 5,wherein the core guide part includes multiple through holes, which eachpass through a circumferential wall of the core guide part in a samecircumference of the core guide part in an axial direction.